The manufacture of paper cups begins with rolls of paperboard stock. In some embodiments, the stock is generally first printed with any graphics or printing that will appear on the finished cup. The printed stock is then coated with polyethylene. Only the inside surfaces are coated if the cup is intended for use with hot liquids. Both the inside and outside surfaces are coated if the cups are intended for use with cold liquids. Coating the outside of cold liquid cups prevents condensation that forms on the outside of the cup from soaking into the paperboard.
After printing and coating, the paperboard stock is die cut into blanks that will become the cup wall. Each blank is then wound around a tapered mandrel to form the cup wall and overlapping wall edges are bonded with heat and pressure.
Disks for the cup bottoms are die cut from (typically unprinted) paperboard stock, and a disk is pressed into the smaller diameter of each cup wall and sealed in place with heat and pressure. In some instances, the upper edge of the cup is rolled into a lip.
Plastic lids are sized and shaped to interact with the upper edge of the paper cups so that a lid of a particular diameter is required to fit a cup having a corresponding upper diameter. Therefore, establishments supplying different sized cups also must supply lids having diameters corresponding to each cup size. This leads to establishments having an increased number of stock keeping units (SKUs) associated with the various sized lids and the various sized cups.
Moreover, the fit between conventional paper cups and plastic lids is not always consistent and/or secure, which can lead to leakage between the cup and the lid and can also result in the lid popping off of the paper cup. This is particularly the case as the paper cup loses its rigidity with use (and sometimes becomes soggy). Although a plastic cup fitted with a plastic lid results in a more consistent fit than a paper cup fitted with a plastic lid, plastic cups are more expensive to manufacture.